They serve totally different purposes, so depends on what you want. As for me, I would rather have the polarizer. A lens hood's function can be replaced with other techniques, but a polarizer's effect is extremely hard (if not impossible) to mimic.

I agree, although in reality you can choose both, if I could only choose one it would be a polarizer. Although a hood can reduce lens flare, flare can be eliminated in post processing unlike the effects of a polarizer.

A lens hood for that lens would weigh almost nothing. It wouldn't really be significant.

I would have one concern for the lens hood. As the lens is a somewhat wide angle zoom, the hood will be rather small and ineffective in the long end of the zoom. So the benefit from having one will be small. It does offer a little extra protection for the front of the lens. If you skip the genuine Canon hood and get a 3rd party one, it will cost a lot less.

The polariser filter isn't usually used in street type photography. More useful for landscapes or other situations where you need reflection control.